THYSANOCRINID^. 193 



a deep notch for the reception of the first interbrachials. Costals about of 

 equal size^ considerably smaller than the radials. Arms ten^ rather stout, the 

 two lower plates, which are included in the calyx, longer than the free plates ; 

 the latter short, arranged in two series, with a few cuneate interlocking joints 

 at the proximal end. Pinnules long, closely packed ; composed of about six 

 remarkably long joints, which are thickest at the ends. First interbrachials 

 as large as the radials ; succeeded by two much smaller plates, and a few 

 still smaller ones above. Anal plate large, resting upon the truncated basal ; 

 succeeded by three plates in the second row. Structure of disk and position 

 of anal opening unknown. Column round, strong, the nodal joints wider and 

 longer, rounded at their edges. 



Horizon and Locality. — Niagara group ; Lockport, N. Y. 



Type in the Museum of Cornell University at Ithaca. 



Thysanocrinus inornatus (Hall). 

 Plate XYIIL Figs. 6a, &, c, d, and XIX. Fig. 5. 



1863. Gli/ptaster inornatus — Hkl-L', Trans. Alb. Inst., Vol. IV., p. 205 ; also 28th Eep. N. Y. State Mus. 



Nat. Hist. (1879, Ed. II., p. 134), Plate 14, Tigs. 1-6; also Iltli Rep. Geol. Surv. Indiana, 



1881, p. 263, Plate 13, Pigs. 1-6. 

 1881. Glyptaster inornatus — ISf. and Sp.; Revision Palseocr., Part II., p. 196. 



Calyx somewhat urn-shaped, the sides shghtly convex ; cross-section at 

 the top of the costals pentagonal, the angles corresponding to the rays ; 

 across the distichals decagonal. 



Infrabasals very minute, only the extreme points of the plates visible 

 beyond the column.* The ornamentation consists of single series of broad, 

 ill-defined radiating ridges or elevations. Some of the more prominent ones 

 follow the median line of the rays; while others take a lateral direction, 

 radiating from the centre of the plates to the margins, where they meet 

 with similar ridges from the interbrachials and basals. 



Basals large, their lower margins thickened and expanded into nodes — 

 one to each plate — which stand on a level with the top stem joint, and 

 form a marked pentalobate rim around it. Eadials larger than the basals, 

 and wider tlian long. First costals considerably smaller and quadrangular, 



* Prof. Hall described tbe "basals" — the infrabasals of modern terminology — as "much developed, 

 distinctly pentangular, with a double or triple node on each plate, and spreading beyond the column." Prom 

 this description we suspect that the author took the nodes at the lower end of the basals for plates, and over- 

 looked the small infrabasals which are rarely observed. We draw attention to this, because Hall, in compar- 

 ing this species with his " Gli/ptaster " occidentalism makes " the greater development of the basal plates " 

 a specific distinction. 



25 



